Concrete Formwork Basics

Formwork for Concrete

• Formwork is a temporary structure that molds and supports freshly poured concrete until it sets and becomes self-supporting.
• Development of formwork has evolved alongside concrete construction in the 20th century due to increased utilization of concrete as a primary construction material.
• Components of formwork, including connections, braces, and anchorages, are also temporary.
• Formwork materials must be durable and maintainable, as they are reused multiple times.

Types of Formwork

• Timber Formwork: Traditionally made on-site from lumber and plywood; labor-intensive with a shorter lifespan. It's flexible and more economical in regions with low labor costs.
• Prefabricated Modular Formwork: Constructed off-site and easily assembled; made from steel, aluminum, or high-density plastics. Offers durability and improved surface finish.
• Stay-In-Place Structural Systems: Utilize prefabricated materials and remain permanently in position post-concrete curing. Suitable for columns, piers, and bridge decks.

Formwork Design and Goals

• Proper design maximizes reuse while ensuring safety and quality.
• Critical objectives include maintaining strength, alignment, and dimensions during and after material placement.
• Forms must be rigid under loads, stable for alignment, and capable of enduring repeated handling.

Economic Considerations and Techniques

• Significant percentages of construction costs are attributed to formwork; planning during bidding is essential.
• Strategies to economize:
  • Design forms for maximum reuse.
  • Use shop-built forms for efficiency.
  • Consider rental options for prefabricated forms.
  • Utilize cranes effectively to handle large load sections.
  • Optimize concrete placement by avoiding high lifts to reduce complications.

Form Materials and Properties

• Plywood is commonly used, known for its economical large panels and smooth surface finish.
• Key properties of lumber, such as allowable stresses, moisture effect, and size adjustments, must be considered in the design of formwork.
• Plywood's performance is enhanced with cross banding, offering strength in two dimensions.

Loads and Forces on Formwork

• Fresh concrete exerts hydrostatic pressure as it behaves like a fluid during placement.
• Factors influencing lateral pressure include concrete mixture density, temperature, placement rate, and use of admixtures.
• Understanding allowable stresses in wood is crucial for ensuring formwork integrity, including adjustments for load duration, moisture, and temperature.

Essential Components of Formwork

• Ties: Hold concrete forms together under fluid pressure; designed for partial or complete removal.
• Anchors and Clamps: Used to support and position formwork against lateral pressures.
• Ensure plywood and lumber are free from defects to maintain allowable stresses and prevent failure during the construction phase.

Explore the fundamentals of formwork used in concrete construction. This quiz covers the types of formwork, their functions, and the importance of temporary molds in shaping concrete. Test your knowledge on how formwork has evolved alongside concrete technology.